The invention relates to a microwave resonator for or on a textile machine, especially a card, draw frame, combing machine or the like, for attachment to a measuring device for measuring the mass and/or moisture content of textile fibre material conveyable continuously through a resonator chamber.
In practice, methods and apparatuses are used to detect at least one property of a material by evaluating the detuning of a microwave-fed HF resonator caused by the presence of the material; a high-frequency signal influenced by the material is tapped off the resonator, and the resonant frequency shift and attenuation of the signal compared with a signal unaffected by the material is determined. The purpose of determining the properties is in particular to obtain signals from materials such as textile fibre material, for example, cotton and/or synthetic fibres, these signals being subject to further processing to give signals corresponding to the mass and/or moisture content of the textile fibre material, which can be used for a control and/or regulation of a textile machine.
In a known microwave resonator chamber used in the monitoring of textile fibre material, a housing with wall elements is present, wherein-through-openings in spaced wall elements lying opposite each other are coaxially connected by a tubular element and the interior space of the housing is hollow. In the case of one known microwave resonator (WO 2005/003747 A), the resonator is arranged in a platform-like supporting construction. The supporting construction comprises for that purpose a cylindrical central recess. A wall element in the form of a flat cylindrical disc with screw seats at its edge that align with complementary blind bores in the supporting construction is positioned on the recess. Hexagon screws are screwed into these bores, which each have an internal thread, in order to screw the wall element to the supporting construction. The wall element positioned on the recess creates a resonator chamber of the microwave resonator into which microwaves are injected by means of an injection means and extracted by means of an output means. Both the injection and output means, which are, for example, of rod form, project from the outside into the resonator chamber through complementary bores in the wall element. A dielectric substantially in the form of a hollow-cylindrical guide tube and comprising an electrically non-conducting material is inserted in the resonator chamber. The dielectric has at each end face an external bulge, with which it lies in a through-opening of the wall element on the one hand and a through-opening in the supporting construction on the other hand. A fibre sliver is guided linearly through the resonator chamber and subsequently through a sliver funnel. The sliver funnel is held in an annular bead of the supporting construction and has an annular groove for that purpose. It is a considerable disadvantage that the central recess for each microwave resonator has to be shaped in the platform-like supporting construction, for example, by a machining process such as milling or the like. This is associated with a considerable amount of time and energy in production terms. Another particular disadvantage is that the wall element (flat cylindrical disc) positioned on the recess forms the closure element for the resonator chamber. The tubular element thus connects the superimposed wall element with the base wall of the supporting construction. Between the wall element and the supporting construction there is a circumferential, circular ring-shaped contact face, which has to be conductively sealed off to avoid interruption of the wall currents and hence a collapse of the microwave field. The electrical fields cause a movement of electrons, i.e. a current flow, at the surface of the inner walls of the resonator chamber. For an optimum behaviour of the microwave resonator, the surface current must flow along the shortest path and with the least possible resistance, as otherwise it builds up an electromagnetic opposing field, which attenuates the resonance field and thus leads to a lower quality of the resonator. The resonator must therefore have on its inside a surface of low peak-to-valley height (short-paths) and good conductivity. The circumferential edge of the flat cylindrical disc is a significant disruptive factor here. In addition, it is impossible to ensure a good and universally uniform contact between the flat cylindrical disc and the supporting construction, so that here too the current flow is impeded or even prevented by poor conductivity or by inadequate contact. Oxidation or contamination of the contact surface is also a possibility. If the electrical connection of individual components of the resonator is not uniform or adequate, however, an undefined behaviour of the resonator may occur under changing climatic conditions. Also, and in particular, total failure is possible, because the resonator can no longer be excited.